Video conferencing systems allow for simultaneous exchange of audio, video and data information among multiple conferencing sites or endpoints. Systems known as multipoint control units (MCUs) perform switching functions to allow multiple sites to intercommunicate in a conference. The MCU links the sites together by receiving frames of conference signals from the sites, processing the received signals, and retransmitting the processed signals to appropriate sites. The conference signals include audio, video, data and control information. In a switched conference, the video signal from one of the conference sites, typically that of the loudest speaker, is broadcast to each of the participants. In a continuous presence conference, video signals from two or more sites are spatially mixed to form a composite video signal for viewing by conference participants. The continuous presence or composite image is a combined picture that may include live video streams, still images, menus or other visual images from participants in the conference.
In a typical continuous presence conference, the video display is divided into a composite layout having areas or regions (e.g., quadrants). Sites are selected at conference setup from the sites connected in the conference for display in the regions. Common composite layouts include four, nine or sixteen regions. The layout is selected and then fixed for the duration of the conference.
Some conference arrangements provide different composite signals or video mix such that each site may view a different mix of sites. Another arrangement uses voice activated quadrant selection to associate sites with particular quadrants. That arrangement enables conference participants to view not only fixed video mix sites, but also a site selected on the basis of voice activity. However, the layout in terms of number of regions or quadrants is fixed for the conference.
Videoconferencing endpoints are capable of sending and receiving video signals with a greater variety of values for picture properties, such as picture aspect ratio and picture resolution. For example, some endpoints can send video signals with a picture aspect ratio of 16:9 or 4:3. While most endpoints can display a picture aspect ratio of 4:3, some endpoints can more optimally display a picture aspect ratio of 16:9. Some endpoints are capable of sending or receiving a small maximum picture size such as 176×144 pixels (“QCIF”) while others are capable of sending or receiving a large maximum picture size such as 1280×720 (“w720p”).